Phase-converter system



Jan. 15 1924.

1,480,713 C. LE G. FORTESCUEY PHASE CONVERTER SYSTEM Original Filed Nov.16, 1918 ATTORNEY J A0 i E5 6 J4 E TZ' WITNESSEG: I INVENTOR i 37% I MAMPatented Jan. 15, 1924.

UNITED STATES PATENT OFFICE.

CHARLES LE G. FORTESCUE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WEST-INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENN-SYLVANIA.

PHASE-CONVERTER SYSTEM.

Original application filed November 16, 1918, Serial No. 262,809.Divided and this application filed February 5, 1921.

To all whom it may concern:

Be it known that I, CHARLES Ln Gr. hon'rnsonn, a subject of the King ofGreat Britain, and a resident of Pittsburgh, in the county of Alleghenyand State of Pennsylvania, have invented a new and useful Improvement inPhase-Converter Systems, of which the following is a specification, thisapplication being a division of my application Serial No. 262,809, filedNovember 16, 1918.

My invention relates to phase-converting systems and particularly tomeans for compensating for the impedance electromotive forces of theconverter. My invention is particularly adapted for railway systems inwhich single-phase energy is distributed through the trolley conductorand converted, on the locomotive, into polyphase energy for energizingthe driving motors.

It is well known that, if a polyphase induction motor or synchronousmotor having a good damper winding is connected to a single-phase line,polyphase electromotive forces will appear at the terminals of themotor. It is also well known that the phases which are not connected tothe single-phase line will be somewhat displaced in phase position andreduced in amount by reason of the impedance of the converter.

The patent to B. G. Lamme, No. 1,243,430, granted October 16, 1917, andassigned to the WVestinghouse Electric & Manufacturing Company,discloses a system for compensating for the impedance electromotiveforces of the converter by providing the single-phase transformerwinding with taps whereby the induced or tertiary electromotive force ofthe converter may be displaced with respect to the phase which isconnected to the single-phase source. In order to avoid discontinuity inthe power supply, while shifting from one tap to another, in the abovementioned system, it is necessary to employ preventive coils, such asare disclosed in the patent of Simmon and Hall, No. 1,232,863, grantedJuly 10, 1917, and assigned to the Westinghouse Electric & ManufacturingCompany.

It is the object of my invention to avoid the necessity for preventivecoils. by utilizing two single-phase transformer windings connected inparallel, the connections being so Serial No. 442,766.

arranged that, when the contactors are disengaged from the taps inpassing from one tap to another, the single-phase coils will beconnected in series with the converter in such manner as to, in effect,reverse the phase sequence of the polyphase electromotive forces.

The series connection of the phase converter constitutes thesubject-matter of a copending application of Lewis WV. Ohubb, Serial No.206,921, filed December 13, 1917, and assigned to the lVestinghouseElectric & Manufacturing Co. In the series system of conversion, theimpedance electromotive forces of the converter are combined with thepolyphase electromotive forces in such manner that symmetry is notdisturbed.

It is, therefore, an object of my invention to produce a shuntphase-converter system in which the transformer tap connections may beshifted to maintain the polyphase electromotive forces in substantiallybalan ied condition withoutthe use of preventive cm s.

Other objects, as well as details of construction, of my invention willbe apparent from the following description and accompanying drawings,wherein Figure 1 is a diagrammatic view of a phase converter connectedin accordance with my invention, whereby the magnitude of the tertiaryelectromotive force may be adjusted,

Fig. 2 is a series of vector diagrams for the various positions of theadjusting devices, and

Fig. 3 is a vector diagram showing the terminal polyphase electromotiveforces corresponding to the first position of the adjusting devices.

In the embodiment of my invention shown in the drawings, I provide asingle-phase transformer 10 having two secondary windings 11 and 12. Myphase converter is shown at 13 as a three-phase induction motor havingmain primary windings 14 and 15, an auxiliary primary or tertiarywinding 16 and a secondary winding 17, shown as being of thesquirrel-cage type.

One terminal of the transformer winding 11 is connected, by means of aconductor 18, to the phase-winding 15 of the converter. The otherterminal of the transformer winding 11 is provided with a plurality oftaps 19 to which the phase-winding lt is selecttively connected by meansof a conductor A and a switch-arm 20.

in like manner, one terminal of the transformer winding 12 is connected,by means of a conductor 21, to the phase-winding 1 1, and the otherterminal of transformer winding 12 is provided with a plurality of taps22 to which the phase-winding 15 is selectively connected by means of aconductor B and a switch-arm 23. The switch-arms 20 and 23 may beconnected to move in opposite directions by means of a connecting link24.

The center taps of groups 19 and 22 are connected to phase conductors Dand F, respectively, of a three-phase load circuit, the other phaseconductor C of which is connected to the tertiary winding 16 of theconverter. The load is indicated inthe drawing as comprising aninduction motor 25 which is connected to the driving wheel 26 of alocomotive.

When the motoring load is increased, it is desirable to increase thesingle-phase electromotive force supplied to the phaseconverter, ascompared with the corresponding electromotive force supplied to the loadcircuit, in order to overcome the voltage-drop in the tertiary voltageof the converter. During recuperation, however, it is desirable toreverse the process in order to maintain balanced polyphase conditions.

hen the switch-arms 20 and 23 are in engagement with taps 19 and 22, thesinglephase windings 11 and 12 are connected in multiple. When theswitch-arms are moved from one tap to another, they are, for a monient,entirely disengaged from the taps. Under the conditions just mentioned,the coils 11 and 12 are connected in series between the phase-windings15 and 14 and the polyphase load conductors D and E, respectively. Theeffect of the series connection is to add a single-phase electromotiveforce to the induced electromotive force of each of the phase-windings15 and 14, making the resultant electromotive force in each case equalto the induced electromotive force in the other of said phase windings.

It will be observed that, when the phase converter is operating as ashunt-connected machine, the winding that is connected to thesingle-phase source has an induced electromotive force which issubstantially equal and opposite to the single-phase electromotiveforce. The corresponding phase of the load is connected to thesingle-phase source and, therefore, the polyphase electromotive forceswhich are impressed upon the load, through the conductors D, C and E,has a phase sequence opposite to the phase sequence of the inducedelectromotive forces of the converter.

lVhen the converter operates as a seriesconnected machine, the polyphaseelectromotive forces which are impressed upon the load still have aphase sequence opposite to that of the induced electromotive forces inthe converter, as above pointed out. It is, therefore, clear that,during the transition periods, when the switch-arms 20 and 23 are movingfrom one tap to another, the converter continues to supply polyphaseenergy, in the same phase sequence, to the load.

The operation of the abovewlescribed apparatus will be more readilyunderstood by reference to Fig. 2. The various sections of thesingle-phase coils are numbered from 1 to 6 in Fig. 1, and the voltagevectors are correspondingly numbered in F 2. Vectors are drawn for eachof the three posilions of the s. In the first position, whichcorresponds to motoring conditions, the single-phase electrometive forceA B, which is supplied to the converter, is greater than thecorresponding electromotive force D E of the load, as shown in Fig. 1and in the top set of vector diagrams in Fig. 2. In the second orcentral position of the switch arms 20 and 23. which corresponds tolight-load conditions, the single-phase electromotive forces applied tothe converter and to the load are equal, as indicated in the middlegroup of vectors in Fig. 2. In the third or reniiaining position of theswitch arms, which corresponds to regenerative operation, the converterreceives a smaller single-phase electromotive force than the load, asindicated in the bottom group of vectors in Fig. 2.

In Fig. 3, I have indicated the tertiary electromotive force vector G F,which bisects the vector AB and which is equal to approximately 0.866times 11B. lit will. be seen that the manipulation of the switcharms 20and 23 will vary the magnitude of the induced tertiary electromotiveforce of the converter, to compensate for the impe dance voltage of thewindings. i will also be understood that, if the voltage AB is increasedbeyond the amount necessary to account for the impedance voltage of thewindings, the load voltage may be increased at the expense of thebalancing of the system.

While I have shown a preferred embodiment of my invention in theappended drawing, 1 do not wish to be restricted thereto, but I desirethat only such restrictions shall be placed upon my invention as are setforth in the appended claims.

I claim as my invention:

1. The combination with single-phase windings and a polyphase circuit,of a phase converter connecting said windings to said circuit forinterchange of power, said windings being provided with taps whereby thevoltage applied to the converter may be varied with respect to thevoltage applied to the polyphase system, switch-arms for sehlvarms 20and lectively engaging said taps, and connections whereby said converteroperates as a shunt-connected machine when said switcharms are inengagement with said taps and whereby said converter operates as aseriesconnected machine during the transition period in which saidswitch arms are disengaged from said taps in passing from one positionto another.

2. In a phase-converting system, the combination of a polyphasedynamo-electric machine adapted to operate as aphase converter, a pairof single-phase transformer windings, a polyphase translating device,connections whereby said single-phase windings are connected in parallelto operate said converter as a shunt-connected machine, said connectionsincluding taps for varying the single-phase electromotive forces appliedto the converter with respect to the singlephase electromotive forcesapplied to the translating device, switch-arms for selectively engagingsaid taps, and connections whereby said single-phase windings are placedin series with the converter when said switch-arms are out of engagementwith said taps.

3. In a system for converting from singlephase power to polyphase power,or vice versa, the combination with a converter having primary,secondary and tertiary windings, of a pair of single-phase windingsconnected in parallel, comr tions for connecting said single-phasewindings in series with the respective terminals of said primaryconverter windings, a load circuit adapted to be connected to the outerends of said singlephase windings and to said tertiary con verterwindings, the outer ends of. each of said single-phase windings beingprovided with taps, and switch-arms connected to the terminals of theprimary converter windings and adapted to engage said taps, whereby theconverter will operate as a shunt-connected machine when saidswitch-arms are in engagement with said taps and whereby said converterwill operate as a series-connected machine when said switch-arms are inintermediate positions between said taps.

4. The combination with single-phase windings and a three-phase circuit,of a phase converter connecting said windings to said circuit forinterchange of power, said windings being provided with taps whereby thevoltage applied to the converter may be varied with respect to thevoltage applied to the three-phase system, switch-arms for selectivelyengaging said taps, and connections whereby said converter operates as ashunt-connected machine when said switcharms are in engagement with saidtaps and whereby said converter operates as a symmetrically connectedseries-converter machine during the transition period in which saidswitch arms are disengaged from said taps in passing from one positionto another.

5. In a phase-converting system, the combination of a polyphasedynamo-electric machine adapted to operate as a phase converter, a pairof single-phase transformer windings, a three-phase translating device,connections whereby said single-phase windings are connected in parallelto operate said converter as a shunt-connected machine, said connectionsincluding taps for varying the single-phase electromotive forces appliedto the converter with respect to the singlephase electromotive forcesapplied to the translating device, switch-arms for selectively engagingsaid taps, and connections whereby said sin le-phase windings are placedsymmetrical l in series with the converter when said switch-arms are outof engagement with said taps.

In testimony whereof, I have hereunto subscribed my name this first dayof February, 1921.

CHARLES LE G. FORTESCUE.

